The phenomenon that a substance emits visible light or light in the vicinity of visible light at a low temperature, e.g., room temperature, when it receives a stimulation from outside is heretofore well known as a so-called phenomenon of fluorescence. Such a substance to cause the phenomenon of fluorescence or, namely, a phosphor, is employed for illuminating lamps such as fluorescent lamps and the like and for displays such as CRTs (cathode-ray tubes) or, namely, so-called Braun tubes, and the like.
The external stimulation to cause the phenomenon of fluorescence is usually given by ultraviolet light, electron beams, radiations such as X-rays, electric fields, chemical reactions and others but no investigations have yet been made for a material capable of emitting light when stimulated by a mechanical external force and the like.
The inventors previously made proposals for a high-brightness stress light-emitting material consisting of a substance formed from an aluminate having a non-stoichiometric composition and having lattice defects emitting light when carriers excited by mechanical energy return to the ground state or a substance containing, in the above matrix substance, rare earth metal ions or transition metal ions as the center ions of the center of luminescence (official publication of Japanese Patent Kokai No. 2001-49251) and a light-emitting material in which the matrix material was Y2SiO5, Ba3MgSiO6 or BaSi2O5 (official publication of Japanese Patent Kokai No. 2000-313878). These luminescence materials are not suitable for practical applications because of their still insufficient luminescence intensity and, in addition, the limitation of the range of the matrix materials to be used so that the application field is necessarily limited.